Fig. 1. A schematic view of intracellular changes in tubular cells upon injury.

Mitochondria undergo metabolic disorders, manifested by decreased fatty acid oxidation. Mitochondria can also produce ROS and further activate the NLRP3/inflammasome. Production of mitochondrial ROS is also related to the expression of proinflammatory factors. ER stress caused by misfolded proteins can start the unfolded protein reaction (UPR), including activation of GRP78 and downstream signaling, including the PERK–eIF2–ATF4 pathway and ATF6 pathway. However, persistent activation of UPR can result in apoptosis. Autophagy plays a dual role. This process can either avoid apoptosis or aggravate renal fibrosis, depending on different situations. Injuries can also lead to epigenetic changes and changes in mRNA expression